Operating in conjunction with a multiplicity of linked sensors, conventional Electronic Control Modules (ECMs) use intake air volume, engine rotation speed, water temperature and other sensor signals to control fuel injection volume in order to optimize the air-fuel ratio for the engine. These sensors are the ECM's eyes and ears and are used to determine how the engine is performing. Based on that information, the ECM can change the fuel-flow rate, spark timing, fuel injection volume, or idle speed to compensate or adapt to various conditions, e.g. standard temperature, fuel grade, or variation in atmospheric pressure at different altitudes.
One important sensor for feedback systems is the oxygen (O2) sensor. This sensor monitors exhaust-gas oxygen content and reports this information to the ECM. The O2 sensor is typically located in the exhaust collector but ahead of any catalytic converter. Typically, the O2 sensor does not activate until about 20 seconds after the vehicle has been cold started. During this time, the fuel injection is controlled on a non-feedback basis, i.e. in a pilot injection. In other words, the fuel injection volume is determined instead by the standard temperature, fuel grade, and atmospheric conditions.
Fuel grade is especially important critical to the performance and driveability of a vehicle. Automotive vehicles are designed to meet a number of requirements, such as those relating to emissions, drivability, and start ability. Despite the setting of strict fuel specification standards and penalties for the sale, transportation, and production of noncompliant fuels, such fuels often remain undetected and find their way to consumers. Attempts to weed out or identify such noncompliant fuels have been complicated due to effects of seasonal changes on fuel properties. The problem is further compounded since several different grades of fuels with their respectively different properties are used, and properties of even the same fuel can vary by season and geographical area.
Amongst the various properties of a fuel, volability is one of the most important. It has tremendous effect on a vehicle's operations, e.g. engine starting, driveability under cold and hot engine conditions, and tendency to vapor lock. Fuels that do not vaporize readily may cause hard starting of cold engines and poor vehicle driveability during warm-up and acceleration. Conversely, fuels that vaporize too readily in fuel pumps, lines, carburetors, or fuel injectors can cause decreased liquid flow to the engine, resulting in rough engine operation or stalling. There are several measures of fuel volatility; two of these are Reid vapor pressure (RVP) and distillation, driveability index (DI).
ASTM defines vapor pressure as “a factor in determining whether a fuel will cause vapor lock at high ambient temperature or high altitude, or will provide easy starting at low ambient temperature.” Vapor pressure is the pressure exerted by vapor formed over a liquid in a closed container. RVP is the pressure measured in pounds per square inch (psi) using a specific instrument heated to 100° F. A lower RVP indicates that the gasoline is less volatile. Additionally, the RVP value determines the start ability of a vehicle; the lower an RVP value, the worse the start ability.
Distillation temperature measurements involve heating a fuel and measuring the temperature at which a certain percentage of the sample evaporates. DI index was developed to indicate gasoline performance during engine cold start and warm-up. The higher the DI value, the worse the drivability. As such, the use of non-compliant fuels has tremendous effects on the performance and driveability of a vehicle.
According to the prior art, fuel injection volume is simply increased so as to improve the start ability and drivability of a vehicle and to compensate for the effects of a non-compliant fuel. However, this imprecise increase of fuel injection volume leads to increased exhaust gas. Hence, the conventional method is an imperfect solution.